Abstract

Melanoma-associated antigen D2 (MAGED2), a member of the MAGE-II cancer testis antigen family, is expressed by almost all normal tissues and many different cancer tissues. Although it has been reported that MAGE proteins have a pro-survival role in cancer cells such as malignant mast cells, the potential biological significance of MAGE proteins in melanoma remains to be established. Here, we show that MAGED2 is involved in the protection of melanoma cells against apoptosis induced by TNF-related apoptosis-inducing ligand (TRAIL) through suppressing the expression of TRAIL-R2, the major TRAIL death receptor that mediates TRAIL-induced apoptosis in melanoma. siRNA knockdown of MAGED2 sensitised melanoma cells to apoptosis induced by TRAIL. This was associated with enhanced activation of the caspase cascade and formation of the TRAIL death-inducing signalling complex (DISC), suggesting that MAGED2 acts at or above the DISC to protect melanoma cells against TRAIL-induced apoptosis. Indeed, inhibition of MAGED2 by siRNA resulted in up-regulation of TRAIL-R2 on the melanoma cell surface, which appeared to be specific, because knockdown of MAGED2 did not impinge on the expression of other TNF receptor family members, nor did it up-regulate TRAIL-R2 in melanocytes. Up-regulation of TRAIL-R2 by inhibition of MAGED2 was mediated by a p53-responsive transcriptional increase, in that p53 was also up-regulated in melanoma cells with MAGED2 knocked down, and that knockdown of MAGED2 did not up-regulate TRAIL-R2 in melanoma cells deficient in p53. In summary, our results identify MAGED2 as an important mechanism that suppresses TRAIL-R2 expression, thus protecting melanoma cells from TRAIL-induced apoptosis.